FIG. 3 shows an example of a structure of a conventional single crystal pull-up device 1.
A quartz crucible 3 is disposed in a single crystal pulling vessel 2, namely a CZ furnace 2. Polycrystalline silicon (Si) is heated and melted in the quartz crucible 3. After the melting is stabilized, a single crystal silicon 6 is pulled up from a silicon melt 5 in the quartz crucible 3 by a pull-up mechanism 4 by a CZ method. When pulling up, the quartz crucible 3 is rotated by a rotation shaft 9.
During a single crystal pull-up process (single batch), various types of vaporized materials are generated in the vessel 2. Accordingly, argon (Ar) gas is supplied into the single crystal pulling vessel 2 and exhausted together with the vaporized materials out of the vessel 2 to remove the vaporized materials from the vessel 2, thereby cleaning it. A supply flow rate of the argon gas is determined for each process of the single batch.
A heat shielding plate 8a (gas rectifying tube) is provided above the quartz crucible 3 and also around the single crystal silicon 6 to rectify the gas in the single crystal pulling vessel 2 so as to guide it to a surface 5a of the melt 5 and to shield the single crystal silicon 6 from a heat source. A distance of the gap between the bottom end of the heat shielding plate 8a and the melt surface 5a is determined appropriately.
Oxygen is in a state of non-solid solution in the pulled-up and grown single crystal silicon 6. The oxygen dissolves from the quartz crucible 3 into the silicon melt 5 and is taken into the single crystal silicon 6 when it is pulled up. The oxygen concentration in the single crystal silicon 6 has a significant influence on the element and device characteristics and also has significant influence on the yield in the element and device manufacturing process. The element and device have various oxygen concentrations which are required depending on their types. Therefore, the manufacturing of single crystal silicon requires a process capable of coping with various oxygen concentrations. At the same time, when the oxygen concentration is more uniform in a growing direction of the crystal, the portion conforming to the oxygen concentration required for the element and device become larger. Therefore, when the control range of the oxygen concentration is increased for the entire crystal, it becomes possible to improve the yield of the single crystal silicon.
A single heater 10 is disposed in a ring shape around the quartz crucible 3. The heater 10 has a positive electrode 11 and a negative (ground) electrode 12 and generates heat when a voltage is applied between the electrodes to heat the melt 5 in the quartz crucible 3. The electric power supplied to the heater 10 is adjusted to change a heat generation amount of the heater 10, so that the temperature of the quartz crucible 3 is changed to change a behavior of oxygen, which is eluted from the quartz crucible 3 and taken into the single crystal silicon 6. Thus, the heat generation amount of the heater 10 has an influence on the oxygen concentration in the single crystal silicon 6.
But, when the single heater 10 shown in FIG. 3 is used, the distribution of the heat generation amount in the vertical direction of the heater 10, namely the temperature distribution of the quartz crucible 3, cannot be changed largely. Therefore, mere adjustment of the electric power supplied to the single heater 10 is virtually hard to provide a uniform oxygen concentration in the growing direction of the single crystal silicon 6 because the control width of the oxygen concentration in the single crystal silicon 6 is very small.
Accordingly, there are conventionally known inventions that provide a plurality of heaters vertically at individual positions around the quartz crucible 3 to increase even somewhat the control width of the oxygen concentration in the single crystal silicon 6 as described in the following Patent Literatures.
Patent Literature 1 discloses a heater apparatus that a heater is vertically disposed at two stages along a side surface of a quartz crucible.
Patent Literature 2 discloses a heater apparatus that a heater is disposed at a side surface and a bottom of a quartz crucible.
Patent Literature 3 discloses an invention that a heater is vertically disposed at two stages along a side surface of a quartz crucible and a ratio of electric power supplied to the individual heaters is limited to a prescribed range to control an oxygen concentration in the single crystal silicon.
Patent Literature 4 discloses an invention that a heater is vertically disposed at three stages along a side surface of a quartz crucible, the individual heaters are determined to have a different electric resistance, electric power is supplied from a common power source to the individual heaters, and heat generation amounts generated by the individual heaters are made different to control the oxygen concentration in the single crystal silicon.                Patent Literature 1: JP-A 62-153191        Patent Literature 2: Japanese Patent No. 2681115        Patent Literature 3: Japanese Patent No. 3000923        Patent Literature 4: JP-A 2001-39792        
And, the methods described below, that control the oxygen concentration by means other than the heater, have been put into practice and known.
1) Method that controls the oxygen concentration in the single crystal silicon by a crucible rotation speed, a pressure in the furnace and a gas flow rate in the furnace.
2) Method that controls the oxygen concentration in the single crystal silicon by providing a magnetic field generation device and applying a magnetic field to the melt in the quartz crucible by the magnetic field generation device.